1. Field of the Invention
The present invention relates to portable electronic devices and, more particularly, to power-limited operation of portable electronic devices, such as portable media players.
2. Description of the Related Art
A media player is normally portable media device that is battery-powered. A media player typically operates to store and play media items for the benefit of its user. One exemplary media player is the iPod® offered by Apple Computer, Inc. of Cupertino, Calif. which has the capability to store and play many different media items (i.e., songs) as well as synchronize its media items with a host computer via a bus connection.
When the media player is connected to a host computer by a bus connection over a cable, power can also be supplied to the media player by way of the cable. For example, when the bus connection is a FIREWIRE connection or a Universal Serial Bus (USB) connection, power is available to be supplied to the media player over the bus connection. However, the available power from the bus connection is typically limited by the associated bus standard. For example, USB specification limits the amount of power drawn from a USB bus, normally, the power limit in terms of current is 100 mA. The available power from the bus connection can be used by the media player to perform various operations. Recently, such power from the bus connection has been used to charge the battery utilized by the media player. However, when the media player is consuming significant power due to its performance of operations, the available power from the bus connection can be exceeded by the media player's performance of operations. In such case, the battery is not able to be charged and can operate in a negative charge environment. In the negative charge environment, the battery's charge is being drained because the power consumed by the media player while performing various operations exceeds the power available over the bus connection. This is particularly problematic when the battery charge level is low. If the battery is not already completely discharged, a negative charge environment might be tolerated for some unknown period of time. However, if the media player's operations continue, the battery will eventually be fully drained in which case the media player would fail.
Thus, there is a need for improved techniques to manage power consumption on a media player so that reliable operation can be achieved.